The two primary methods of providing straight or flattened steel strip or sheet are roller leveling and stretcher leveling. Roller leveling is typically performed in a rolling machine consisting of two sets of rolls. A top and bottom set of several small diameter horizontal rows each are mounted in a housing so that the associated top and bottom rolls are offset from each other. A steel sheet or strip passing through the leveler is flexed up and down alternately between the offset rolls such that the amount of flexing decreases as the sheet travels toward the exit end of the roller leveler. The rolls nearest the exit end are designed to perform the basic straightening operation. The advantage of roller leveling is that long lengths of sheets or strip may be leveled or flattened with minimum surface disfigurement. However, roller leveling does not impart the same degree of flatness to the sheet or a pair of opposing jaws actuated by hydraulic or pneumatic means. Typically, sheet or strip is elongated between one and three percent so that the elastic limit of the steel is exceeded to produce permanent elongation. There are numerous types of stretcher leveler devices including those which can handle large coils of rolled strip. However, in all stretcher levelers the jaws of the device include gripping means to securely grip the opposing ends of the sheet which is to be stretched. These gripper means typically comprise a flat elongated engagement member shaving a length slightly greater than the width of the sheet or strip to be stretched. The surface of the engagement member which is adapted to engage or grip the surface of the sheet or strip to hold it against movement during elongation is very rough, normally grooved, knurled or serrated. Consequently, in virtually all such stretcher leveler devices the gripper means bite into the metal and disfigure the surface of the sheet. Traditionally, the disfigured portion of the sheet or strip is marked and subsequently cut off as scrap. For example, in a coil 2,125 feet in length, approximately 162" are lost in scrap.
The disfigurement of the metal results in substantial economic loss because that metal is normally discarded as waste. Moreover, when coils of rolled strips are stretched in sequential stretching, the gripper disfigurement marks must be indicated and cut from the coil. Thus, the maximum length of strip or sheet which could be leveled is the distance between the grippers.
It is, therefore, an object of the present invention to provide a gripper means for use on stretcher leveler devices which affords adequate gripping capabilities, but which eliminates surface disfigurement on the sheet or strip stretched. A further object of the present invention is to provide gripper means which will enable stretching of any length of strip by successive stretching operations such that an entire coil of rolled strip, in effect, can be stretcher leveled without the need to remove the portions of metal engaged by the gripper.